#include <iostream>
#include <cstring>

int main(int argc, char* argv[])
{
    if (argc != 2)
    {
        perror("can not execute!");
        exit(1);
    }
    if (strcmp(argv[1], "-a") == 0)
    {
        std::cout << "hello a!" << std::endl;
    }
    else if (strcmp(argv[1], "-b") == 0)
    {
        std::cout << "hello b!" << std::endl;
    }
    else
    {
        std::cout << "default!" << std::endl;
    }

    return 0;
}